1. Field of the Invention
The present invention relates to apparatus and method for controlling a stepping motor, and an image reading apparatus, and more particularly, it relates to a technique regarding speed-up and speed-down (hereinafter “acceleration/deceleration”) and fixed speed control of a stepping motor used in an original conveyance controlling apparatus of a facsimile, an original reading sensor shift controlling apparatus of a copying machine or a sheet feed controlling apparatus of a printer.
2. Related Background Art
As a motor for controlling conveyance of an original in a facsimile or a motor of a reading portion in original reading sensor shift control in a copying machine, a stepping motor has conventionally been used. In control of the stepping motor, interruption output or trigger output to a CPU and a stepping motor control unit was synchronized with the interruption on the basis of one-line of an image, i.e., one step of the stepping motor, thereby effecting drive control of the motor.
Further, when an exciting current for the stepping motor was determined by using PWM output, since the number of bits of the PWM output was fixed in dependence upon hardware, the motor driving suitable for an image to be read could not be attained. Further, in acceleration/deceleration data tables for effecting phase control of the stepping motor, the number of the tables and the number of steps were fixed.
As mentioned above, in the original conveyance control in the facsimile or the motor control of the reading portion in the original reading sensor shift control in the copying machine, the drive control was effected by synchronizing the interruption output or trigger output to the CPU and the stepping motor control unit with the interruption on the basis of one-line of the image, i.e., one step of the stepping motor. However, in such drive control, there arose a problem that a burden of software processing was increased. For example, as a reading speed for the original was increased, an interval for interruption processing to the CPU was shortened, and a ratio of interruption routine of software was increased or other software processing time was increased.
Further, since the number of bits of the PWM output for determining the exciting current of the motor was fixed, the number of bits of the PWM output could not be changed. Thus, when a color image or an image having high resolving power was read at high speed in a highly fine manner (instructed from an operating portion (not shown)), there arose a problem that a smooth current wave form could not be formed and smooth motor driving could not be attained. Further, in the acceleration/deceleration data tables for effecting the phase control of the motor, since the number of the data tables was fixed, even if the number of data tables was not required, program data corresponding to the number of data tables was required. Further, since the number of steps of the data table was fixed and a condition of a data table number could not read, if acceleration/deceleration control exceeding the number of acceleration/deceleration data tables was effected, renewal portions of a data table register and a present data table number had to be grasped by software, which made software processing more complicated.